JP2008-248474A (Patent Document 1) describes an automatic faucet. This automatic faucet comprises a built-in generator in a device body, and is adapted to generate electrical power by the flow of water to be spouted from the faucet device. The electrical power generated by the generator is used for driving a solenoid valve adapted to switch between water stopping and water spouting of the faucet device.
When it becomes possible in this way to have a built-in generator and to open and close the solenoid valve by electrical power of the generator, it becomes possible to install an automatic faucet configured to sense a user's finger with a sensor and, based on which, to open and close the solenoid valve to switch between water stopping and water spouting, without using an external power source. The automatic faucet which does not require any external power source provides significant advantage that it can be installed without choosing power source environment for the installation location because it operates by simply substituting for an existing faucet device that is installed in a washroom etc.